You probably could solo warbringers with some lfr gear as protection but I have no experience of it.
I've had alot fun soloing old vanilla and tbc raids, even naxx 25 from wotlk as retribution.
Haven't played pvp at all but damage seems pretty low compared to other classes but offhealing is good.

Paladins are better raid tanks in every way (my opinion)
Dks are better at soloing, pvp and old content.

If your dk is a one man army at solo pvp, then my monk at pvp is Chuck Norris riding on a Tyrannosaurus Rex who shoots laser beams from its eyes.

I honestly have both and my ww monk is parsecs better than my dk which has now been shelved and I also never a lost a fight with a dk of any spec. Only things that get me on my ww is BM huntard and very good mage, where as on my dk played as frost as unholy, I would lose to more classes.

Rets are really bad at pvp once you encounter ppl who know they must lock you down when you pop wings.

I would advise the OP to consider dk if he must really choose between ret and dk.

I dont realy know about PvE lately what is best but when it comes to PvP. DK's are a little better Both tanking and DPSing. that said Paladins are not useless so if you like the paladin play style you can easy play with that. I met a bit of Ret paladins in RBG's lately I play around 1900 rateing. But agien DK's are just a little better atm

But every patch changes things so realy jsut stick with the play style you perf

---------- Post added 2013-06-15 at 10:31 PM ----------

Originally Posted by Khorine

If your dk is a one man army at solo pvp, then my monk at pvp is Chuck Norris riding on a Tyrannosaurus Rex who shoots laser beams from its eyes.

Difference between DK and paladin solo'ing capabilities vary, simply put, their biggest advantage right now is actually their ghoul and army, at these low vengeance levels that's enough to give them an edge, along with pushing a lot of DPS into that period of time. Example would be Mione on HM Rag pushing a p3 in one meteor without necessarily vengeance stacking, while I barely beat a third whilst stacking in literally every piece of fire available. Beyond that our DPS difference was negligible.

Other than that the actually situation varies, a fight like Rag once again, paladins have a distinct advantage in being able to chew up a lot more of the magic damage that goes around, primarily stacks. You'll note in Mione and that other DK's kill (god of mmo guy) that they would consistently reset stacks using ghouls, bloodworms and the like. Paladins couldn't do that but luckily don't need to.

As Mione put it herself, part of the reason DKs are still dominate is that she plays them and her gear is always at the cutting edge of what she needs to keep pushing the boundaries.

Mione really said this? Maybe Mione should refrain from buying herself some new hats for a while or else she may find them a little too big in the near future...

I won't link it, just because I don't want to derail the thread, you can find it quite quickly on her latest posts. Don't read too much into it though, I personally see it less as a 'I'm fucking brilliant' and more as simply stating the fact that few others in her position are as invested in solo'ing raid content as she is. She's a main spec DPS (so she'll always be pushing the classes limits) in one of the world's top 25 mans playing a spec that was up until recently above and beyond any other classes capabilities.

PVE they are great healers in raids and the best tanks.
PVP they are amazing healers in arenas / RBGs and always in demand.
PVE dps ret is the best its every been
PVP ret is a juggernaut on the battlefield atm and only getting better with 5.4. Great burst, awsome mobility,crazy offheals and a 6 sec stun every 30,-- How are ya.